In present-day automobile finishing, different substrates are painted, such as bodies and bodywork parts produced from metal or plastic, for example. Frequently in such applications, multicoat paint systems are constructed. Multicoat paint systems on metallic substrates consist frequently of an electrodeposition coat, a primer-surfacer coat, a basecoat, and a clearcoat. In the case of plastics substrates, either single-coat finishes or, again, multicoat paint systems are constructed. In the latter case, the customary primer-surfacer, single-coat topcoat, basecoat and clearcoat coating compositions that can be employed in the painting of plastics are employed, the selection and use of these compositions being known to the skilled person.
The high technological requirement which is imposed on finishes in the segment of the present-day automobile industry, and also the functions and technological properties of each of the individual coats identified above, are known to the skilled person. In such systems it is the clearcoats in particular that define such essential technical properties as, for example, the gloss and the brilliance or distinctiveness of image (DOI), the weathering stability, and also the resistance to condensation and blushing of the painted surface. Key to these properties is that the clearcoat coating compositions necessary for the construction of clearcoats have outstanding application properties. This means, in particular, that the coating compositions must have good leveling. This implies that the clearcoat coating compositions must have flow properties such that, following their application to a substrate, unevennesses which have come about, for example, as a result of spray mist are evened out and hence the surface of the resulting finish is smooth. Likewise important, moreover, is that the coating compositions have a good sag behavior. As the skilled person is aware, following the application of coating compositions to a substrate, there is a risk of runs forming as long as the coating compositions are still in the liquid state. This means that the applied coating compositions, still liquid, undergo partial sagging. The result is a very visible finishing defect in the subsequently cured finish. The tendency to form runs increases disproportionately with the selected wet film thickness, which must therefore be selected appropriately. However, it cannot be selected to be too low, so that complete coverage of the substrate surface is ensured and so that the surface quality requirements are met. In the finishing of articles of complex shape, such as are frequently encountered in the context of automobile finishing (e.g., bodywork, doors or bumpers), the problem of formation of runs occurs more frequently, since in this case it is not possible to paint the entire surface in the horizontal position.
A further problem that plays a large part in the automobile finishing segment in particular is the circuit-line stability of the coating compositions. As a result of their continual revolution in the application plants, the coating compositions are exposed to continual loading or shearing stress, which frequently results in a significant change to the rheological properties, such as the viscosity, and hence may adversely affect the applications properties referred to above.
The existing solvent-containing clearcoat coating compositions are frequently not able to ensure effective leveling and at the same time to prevent the formation of runs in the clearcoats produced from them. To solve the problems, the automakers frequently reduce the film thickness of the clearcoats, but this greatly detracts from such essential performance properties as topcoat holdout, leveling, gloss, distinctiveness of image, and weathering and UV stability, and can lead to matting of the clearcoats. On the part of the clearcoat manufacturers, attempts are made to avoid the problems by adding sizable amounts of rheological assistants or of rheology-control additives, such as the sag control agents (SCA) that are known from the applications WO 94/22968 A 1, EP 0 276 501 A 1, EP 0 249 201 A 1 or WO 97/12945 A 1 and which are based, for example, on particular urea adducts. Likewise used are the crosslinked polymeric microparticles, as disclosed in EP 0 008 127 A 1, for example, the inorganic phyllosilicates such as aluminum magnesium silicates, sodium magnesium and sodium magnesium fluorine lithium phyllosilicates of the montmorillonite type, the silicas such as Aerosils, or the synthetic polymers having ionic and/or associative groups, such as polyvinyl alcohol, poly(meth)acrylamide, poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic anhydride copolymers or ethylene-maleic anhydride copolymers and derivatives thereof, or hydrophobically modified ethoxylated urethanes or polyacrylates. Such use, however, may result in a deterioration in the topcoat holdout, because, for example, the leveling of the clearcoats is adversely affected.
The use of polyamides as thickeners for solvent-containing coating materials is known from the textbook “Lackadditive” by Johan Bieleman, Wiley-VCH, Weinheim, N.Y., 1998, page 62, and also from the application WO 04/11139.
It is additionally known, from technical data sheet 11.20.3 from C. H. Erbslöh, DISPARLON 6900-20X, October 1986, for example, that swollen particles of synthetic polyamide wax can be used as antirun/antisettling agents for solvent-based resin systems (e.g. clearcoats), solvents, high-build coatings of epoxy resins, tar/epoxy resin mixtures, tar/polyurethane mixtures, and chlorinated rubber, aluminum pigments in automotive paints, heavy pigments in rustproofing coatings and carpet-backing coatings, and gel coatings (glass fiber-reinforced plastics). Patent application WO 2004/111139 A1 uses a combination of a hexylamine-based urea compound and polyamide wax particles as a rheological assistant. However, even through the use of these swollen particles of synthetic polyamide wax, or a combination thereof with the stated urea compound, it is not possible to provide a satisfactory solution to the problems addressed above and to achieve a good balance of applications properties such as leveling and formation of runs in tandem with a high stability toward shear stress, and also coating properties such as, for example, good condensation resistance.
It is an object of the present invention, therefore, to provide a clearcoat coating composition which no longer has the disadvantages of the prior art, but instead exhibits an outstanding balance between the application properties of leveling and formation of runs, so that the clearcoat which results after curing on a substrate has a high optical quality, e.g. a high gloss. In addition, the cured coatings are to exhibit high resistance to condensation and blushing. Also, moreover, further important technological requirements are to be met that are imposed on coating materials for use, in particular, in the automobile finishing segment. The clearcoat coating materials are in particular to possess good circuit-line stability or stability under shearing stress, which means that their profile of rheological properties, more particularly their viscosity, is not to undergo excessive alteration in spite of exposure to shearing stress. In this way, the applications properties identified above are to remain intact despite prolonged revolution in circuit-line systems, for example.